It is generally known that radar or ultrasonic detection techniques may be used with a variety of applications, for example, with a reversing radar, with a motion-sensing lighting device, or with other monitoring devices. Such known detection techniques use a device to generate a vibration with a specific frequency and transmit an ultrasonic wave to perform a detection. The ultrasonic wave may arrive at a corresponding target object, reflect off the target object, and the reflected wave may be received by the device, such that the elapsed time from transmitting to receiving the ultrasonic wave may be known as a Time of Flight (abbreviated as TOF). The TOF may thereby be used to calculate a distance from the device generating the ultrasonic wave to the target object. As such, it is possible to perform a detection and make a determination in various environments for related applications.
With reference to the schematic diagrams shown in FIGS. 1A and 1B, a known ultrasonic detection device 10 is illustrated that operates in a detection wave transmission mode and in a reflected wave reception mode, respectively. As shown, the ultrasonic detection device 10 can simultaneously have functions of transmitting an ultrasonic wave and receiving its reflected wave. Accordingly, the device 10 includes a transceiver module (or antenna), which is constituted by a transmitter and a receiver, and the transmitter and receiver can carry out a detection operation in the same direction or toward the same target object 12.
Specifically, the ultrasonic detection device 10 may transmit an ultrasonic wave (detection wave) W11 in the transmission mode and then switch to the reception mode, so as to receive the reflected wave W12 from the target object 12 or another obstacle appearing in front of the device, based on the situation of the reflection received. Therefore, performing a single detection comprises transmitting a detection wave once, switching to a reception mode, and receiving a reflected wave once. Commonly, an ultrasonic detection device may be provided with one or more transceiver modules. If a device has multiple transceiver modules, it is possible for the respective transceiver modules to alternate functions, thereby performing a detection in turn. If a device has only one transceiver module, a mode switch must be performed immediately after a transmission mode so as to carry out a reception.
With reference to FIGS. 2A and 2B, schematic diagrams are provided that illustrate signals that vary over time in situations where there is an obstacle in front of the device (FIG. 2A) and where there is no obstacle in front of the device (FIG. 2B). In the figures, a horizontal axis represents the time and a vertical axis represents a signal level (in volts). As shown, the ultrasonic detection device 10 may first generate an instruction signal S10 to start a detection operation and then generate an oscillating signal S11, which thereby transmits the ultrasonic wave (detection wave) W11, as mentioned above. If an obstacle is located in front of the device, an echo signal S12 (as shown in FIG. 2A) represented by the reflected wave W12 will be received, and if no obstacle is located in front of the device, no echo signal (as shown in FIG. 2B) will be generated.
In this process discussed with reference to FIGS. 1A-2B, a time interval during which the oscillating signal S11 is generated is a type of ringing time, that is, the elapsed time that a piezoelectric patch in the transceiver module gradually turns into a stationary state after generating an ultrasonic wave in the manner of vibration. However, in a practical operation, the ultrasonic detection device 10 may often cause a detection error due to an affection from an external correlated interference source. For example, as shown in FIG. 3A, a schematic diagram illustrates an ultrasonic detection device 10 performing another detection operation with respect to a target object 12, but an interference source 13 is present in the environment (such as a siren, a horn, and other kinds of sounding sources). Thus, in the case of the detection of the detection wave W11, besides the corresponding reflected wave W12 as shown in FIG. 1B, the ultrasonic detection device 10 may also receive a clutter wave W13 emitted from the interference source 13, so making it difficult to correctly determine which one is the reflected wave caused by the target object 12.
Further, with reference to FIG. 3B, a schematic diagram shows a signal that varies with time where other interference sources are located in front of the device. As shown in FIG. 3B, the clutter signal S13 caused by the clutter wave W13 or other interference sources appears the same as an echo signal, making it is impossible for the ultrasonic detection device 10 to distinguish which one represents the reflected wave formed by the target object 12 or which one represents the noise caused by the interference sources, and moreover, making it is difficult to determine the accurate reception time, which influences the corresponding distance calculation.